1. Field of the Invention
The present invention relates to an optical recording medium and, in particular, to an optical recording medium comprising three or more recording layers.
2. Description of the Related Art
An optical recording medium such as a CD (compact disc) or a DVD (digital versatile disc) has been widely employed as a recording medium for recording digital data. In order to increase storage capacity in such an optical recording medium, a multi-layer optical recording medium has been developed, in which a data recording layer has a multilayer structure. In such a multilayer optical recording medium, the recording layers are laminated with an optically transparent spacer layer sandwiched therebetween.
In the above multilayer optical recording medium, upon reproducing a recording mark on a recording layer, light components reflected from the other recording layers are generated. If the amount of the reflected light components or the distance between the recording layers is changed for any reason, the variation (hereinafter referred to as a crosstalk variation) is superposed on the reproduction signal as noise.
In order to reduce the effect of the above-described interlayer crosstalk, an optical recording medium, for example, disclosed in Japanese Patent Laid-Open Publication No. 2004-213720 has been proposed in which each of the recording layers is provided at different interlayer distances.